With the continuing and ever-increasing interest in the recycling of materials from consumer and industrial waste, the secondary aluminum industry continues to be viewed as an important and significant means of preserving and obtaining maximum benefit from a valuable natural resource. The secondary aluminum industry uses a variety of methods and technologies to recover usable aluminum metal from various types of aluminum scrap and other aluminum-bearing waste materials.
One such method is the melting of the aluminum in the waste material while the material is in contact with a molten salt flux. The salt is either 100% NaCl or NaCl and up to 60% KCl. The preference for NaCl may be attributed to its lower cost, and the inclusion of KCl is a means of lowering the melting temperature of the flux. In either case, with sufficient agitation and a sufficiently fluid flux, the molten salt wets the impurities in the waste material and in so doing causes the aluminum to separate from both the flux and the impurities originally present in the aluminum. The flux also protects the melted aluminum, preventing it from becoming oxidized in the furnace itself. The separated aluminum forms droplets which coalesce to form a liquid aluminum pool beneath the molten salt, and this pool is readily drawn off as highly pure aluminum suitable for use in aluminum sheet mills, for the preparation of alloys, and all other types of aluminum processing.
The remaining flux together with the impurities retained with it are typically disposed of in landfills or dumps in a manner which conforms with environmental standards. The potential for environmental contamination remains, however, since NaCl may contaminate aquifers and water tables. A further concern is that the number of appropriate disposal sites is diminishing, and the cost of the use of these sites continues to increase.
These and other problems are addressed by the present invention, which provides a modification of the flux in a manner which produces spent flux which is not only safely disposable but also useful in an environmentally acceptable manner.